A spokesperson for Magellan Midstream Partners, which operates pipelines and oil storage facilities in and around Cushing, said the company had shut down its operations there to "check the integrity of our assets."

"We did not encounter any damage associated with [the earthquake]," he wrote in an email, saying the company expects to resume normal operations on Tuesday.

This is not the first significant earthquake to damage central Oklahoma. The governor declared a state of emergency in September after a magnitude 5.3 temblor.

As we have reported, the USGS announced earlier this year that pumping wastewater underground during oil and gas production has caused parts of Oklahoma and Texas to be as seismically active as parts of California.

"This little patch of prairie in northwestern Oklahoma is one of the most important places in the U.S. energy market. ...

"The massive hub in Cushing, where domestic crude oil enters the energy market, is dotted with hundreds of airplane hangar-size tanks that hold an estimated 54 million barrels of oil.

"No earthquake damage has been reported — yet. But the possibility is a matter of national security.

" 'I have had conversations with Homeland Security. They're concerned about the tanks mostly,' says Daniel McNamara, a U.S. Geological Survey research geophysicist."

Last year, Reuters reported that one company with storage facilities in Cushing, Phillips 66, had changed its protocols to reflect the increased earthquake activity. The changes include new plans for "inspecting the health of crude tanks, potentially halting operations after temblors and monitoring quake alerts."

State regulators in Oklahoma have also tried to reduce the risk of future earthquakes by shutting down or reducing activity at wastewater wells in the area.

Energy companies produce toxic wastewater during oil and gas production. To keep it from contaminating drinking water near the surface, they inject the wastewater into deep disposal wells, which can put pressure on faults in the earth's crust, causing them to slip. The slipping can cause an earthquake.

After a series of earthquakes near Cushing, Oklahoma regulators ordered oil companies in 2015 to shut down all disposal wells within 3 miles of the center of the quake activity and reduced the volume of wastewater being injected into the earth by 25 percent for a radius between 3 and 6 miles from the center. In all, the earthquakes led to changes in the operation of 13 wastewater wells.

Last week, the agency in charge of regulating the state's oil and gas industries, the Oklahoma Corporation Commission, shut down more wastewater wells north of Cushing, after a magnitude 4.3 earthquake shook the town of Pawnee.

The strongest earthquake to hit Oklahoma in nearly five years shook the state Saturday morning, rousing some residents from a dead sleep. It was felt as far north as Nebraska and as far south as Texas.

Updated 6:30 p.m.

Gov. Mary Fallin declared a state of emergency for Pawnee County after the 5.6 magnitude earthquake struck the state Saturday morning, damaging buildings across north-central Oklahoma.

From StateImpact Texas: President Obama’s rejection of the Keystone XL pipeline provoked cheers from environmental groups, boos from rival politicians and a little bit of head scratching in the State of Texas.

Listen

Listening...

/

A story from KUT's Mose Buchele that aired on NPR's All Things Considered.